Method and structure for reinforcing an earthen excavation



Jan. 20, 1970 scH BE JR 3,490,242

ETHOD AND STRUCTURE FOR REINFORCING AN EARTHEN EXCAVATION Filed March 7, 1968 2 Sheets-Sheet. 1

INVENT OR HARRY SCHNABEL JR.

Evi w,WmwA-L ATTORNEY3 H. SCHNABEL, JR

METHOD AND STRUCTURE FOR REINFORCING AN EARTHEN EXCAVATION 2 Sheets-Sheet I INVENIOR HARRY SCHNABEL JR.

Jan. 20, 1970 Filed March 7, 1968 United States Patent 3,490,242 METHOD AND STRUCTURE FOR REINFORCING AN EARTHEN EXCAVATION Harry Schnabel, Jr., 7010 Longwood Drive,

Bethesda, Md. 20034 Filed Mar. 7, 1968, Ser. No. 711,393 Int. Cl. E02d 5/74; E21d 21/00 US. Cl. 61-39 15 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The instant invention relates to earth excavating and more particularly to reinforcing the side faces of excavations to support the surrounding earth. In particular, the invention is applicable to excavations made incident to construction of building foundations and the like.

When such excavations are made, their side walls must be reinforced to preclude the surrounding earth from shearing off along sloping planes of rupture (planes of earth slippage) and falling into the excavation. In this respect it is to be recognized that such shearing (or slippage) if allowed to occur, would at least increase the amount of earth removal required and could result in collapse of adjoining streets, alleys, or the like.

Conventionally, the reinforcement of such excavations has been accomplished by first inserting a plurality of steel soldier piles into the earth around the periphery of the area to be excavated. During excavation, horizontal lagging is installed between the piles. Generally, the piles and lagging must be further braced, which has commonly been accomplished by attaching horizontally extending wales between the piles and installing a plurality of angularly disposed rakers between the bottom of the excavation and each wale. Manifestly, such rakers must be installed prior to removal of all of the earth from the excavation and trenches are dug for this purpose. Thereafter, the rakers while providing the required support, interfere with both the process of excavating and the construction following excavation.

More recently, the problem has been attacked by the use of prestressed tie-backs behind the sheeting wall. Such tie-backs have been effective in reducing the costs of the excavating process itself, by eliminating the use of rakers in the excavation. However, the cost of the tie-backs installation usually exceeds the cost of equivalent rakers by an amount greater than the saving in excavation and subsequent construction costs. Furthermore, tie-backs frequently are not usable where the foundations of buildings on adjoining land are near the property line. In such cases there is insufficient room for the tie-backs which have been required to be anchored behind a theoretical slippage plane which intersects the sheeting wall at the bottom of the excavation and extends angularly upwardly therefrom through the earth behind the wall.

SUMMARY OF THE INVENTION It is a primary object of this invention to provide an excavation reinforcement method and structure wherein advantages of prior art methods are gained while the disadvantages of such methods are eliminated or minimized.

An important object of the invention is to provide a method and structure for reinforcing an earthen excavation which finds wide application and reduces the cost of such an excavation.

Briefly, the invention contemplates a method of shoring a sheeting wall which reinforces an upright earthen face adjacent an excavation and the resulting structure. The upper portion of the sheeting wall is internally supported by a plurality of tie-backs. Each tie-back includes an anchor disposed in the earth placed behind the wall, and a tendon extending angularly downwardly into the earth behind the wall connecting the upper portion of the wall to the anchor. The tie-backs are installed by emplacing the anchors in the earth and then connecting the tendons between the anchors and the upper portion of the sheeting wall. The lower portion of the sheeting wall is externally braced by a plurality of rakers placed between the bottom of the excavation and spaced locations along the lower portion of the wall. These raker connections to the wall are placed above the bottom of the excavation. The rakers extend angularly downwardly from the sheeting wall into the excavation, and have sufficient compressive strength to raise the vertical plane of earth slippage from its normal location along a first plane intersecting the sheeting wall at the bottom of the excavation to a second plane intersecting the sheeting wall at or near the raker connections to the wall. Each of the anchors are emplaced with at least a major portion thereof positioned between the first nad second planes described above.

BRIEF DESCRIPTION OF THE DRAWINGS The invention having been generally described a specific embodiment will be discussed in detail with reference to the accompanying drawings in which:

FIGURE 1 is a fragmentary front elevational view of a vertical excavation face reinforced in accordance with this invention; and

FIGURE 2 is a vertical sectional view taken along line 2-2 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT An earthen excavation which has been constructed and reinforced by the method and structure of this invention is broadly designated in the drawing by the numeral 10 (FIGURE 2). Excavation 10 presents a substantially horizontal subgrade surface or bottom 12 and a substantially upright face 14 which extends upwardly from bottom 12 to a line 16 at grade level which defines the upper peripheral boundary of excavation 10. Although .only a single face 14 is illustrated in the drawings, the peripheral boundary of the excavation will generally be defined by a plurality of upright faces. While the invention will be described with reference to the single face 14, manifestly, each face of the excavation may be reinforced in accordance with the invention. In the description, the terms earthen or earth, are used herein in their broad sense and are intended to include rock strata, soil or clay, and all other ground formations. v

Basically, the excavation face 14 is supported (or reinforced) by a plurality of side-by-side, horizontally spaced, upright steel soldier piles 18 which may take the form of H-beams. The piles 18 are conventional and include flanges 18a for holding a plurality of Wooden lagging members 20 in place against face 14. The members 20 may be short sections disposed behind the outer flanges 18a. Alternatively, the members 20 may be longer see:

tions extending outside of the side flanges and connected thereto by studs. The lagging 20 supported by the piles 18 prevent slippage of the earth 22 from behind face 14 into the excavation in the conventional manner.

Without reinforcement, the earth 22 behind face 14 would tend to shear along a theoretical plane of slippage 24 and fall into excavation 10. The theoretical plane of slippage 24 extends along the angle of repose of the earth material and its location can be determined approximately for any particular site by well-known methods taking into account such criteria as type of material, loading, moisture control, and the like. The plane 24 extends upwardly through earth 22 from the line of juncture 26 between the bottom surface 12 of the excavation and upright face 14. The piles 18 along with the lagging members present a sheeting wall 27 which is substantially coextensive with and bears against face 14. However, wall 27 alone does not provide adequate support against horizontal forces and therefore must be further supported against such forces.

The piles 18 are interconnected by a plurality of elongated, vertically spaced wales 28, 30, and 32 which extend horizontally of face 14, outside of piles 18. The wales 28, 30, and 32 may be constructed of steel or the like and are preferably attached to piles 18 by welding.

The lower wale 28 may be an H-beam and is disposed against the lower portion 36 of wall 27. As shown, the wale 28 is at a point about one third of the distance from the bottom of the excavation to the top of the wall, but theijheight of the wale 28 may vary. Normally, however, the ,wale would be located in the lower third of the wall. A generally horizontal row of elongated, side-by-side, horizontally spaced, angularly disposed rakers 38 are positioned to extend between surface 12 and wale 28. Each raker 38 may be welded to wale 28 and each is anchored to surface 12 by a footing 40 which may be concrete. The rakers 38 have sufficient compressive StllQl'lgth to provide support for the lower portions 18b of piles 18 against vertical displacement and thereby provide external support for lower portion 36 of wall 27. The. compressive strength of the rakers must be sufficient to raise the theoretical plane of slippage to the plane 42 which extends upwardly through the earth from a positionat or near the connection between wale 28 and wall 27.

As shown in FIG. 2, the upper portions 18c of piles 18, and therefore the upper portion 43 of wall 27, are internally supported by a plurality of elongated, side-bysidefhorizontally spaced, angularly disposed tie-back elements 44 interconnected respectively with each of the upper wales and 32. It is to be appreciated that the number of wales such as 30 and 32, which are necessary fonsupporting a given wall depends on the dimensions of Ethe wall itself, its loading and other factors. Thus, although in the preferred embodiment two wales are shown, the invention broadly contemplates usage of only a sihg'le wale or more than two to which tie-backs are connected. Moreover, if a tie-back is used near each soldierpile, the wale or wales may be discontinuous.

Wales 30 and 32 present angularly disposed bearing faces ;46 and 48 respectively. The tie-back elements 44 eacli, include a tendon 45 extending inwardly and downwardly through earth 22 from faces 46 and 48 to positions. beneath and behind plane 42 where each tendon 45 is embedded in an anchor 50 of concrete or the like. A connector 52 is provided to attach each tendon respectively {to the appropriate bearing face 46 or 48. Further, each" tendon extends through a corresponding hollow pipe 54 which terminates adjacent slippage plane 42 as illustrated, although the use of such ahollow pipe is not essential. 'Desirably the tendons 45 are placed in substantial tension when they are installed.

In the illustrated structure, each anchor 50 is elongated and extends from a position near plane 42 toward plane 24 in general alignment with the corresponding tendon 50. Each anchor 50 includes a transverse flange 51 on the corresponding tendon 45 for rigidly interconnecting the anchor 50 and the tendon 45. It will be appreciated that although anchors 50 are shown as being disposed entirely above plane 24, the same might, under some circumstances, extend beyond "plane 24. Further other forms of anchors may be used. For example an enlarged opening may be formed at the end of each tendon and simply filled with concrete. The important factor is that the anchors 50 have at least a major portion thereof positioned between plane 24 and plane 42. Thus, at least a 'major proportion of the internal support for wall 27 is provided by connection of the tie-backs to the earth between planes 24 and 42. This earth would not support such connections unless the plane of earth slippage was raised from 24 to 42 by the external rakers 38 according to this invention. Usually the anchors 50 and tendons 45 are positioned in a pair of vertically spaced mutually parallel planes.

In the practice of the method of the present invention, the line 16 is laid out at the periphery of the excavation 10 which is yet to be dug. The piles 18 are then driven into the ground at appropriate intervals along line 16. Excavation is begun within the confines of line 16 and as upper portions of piles 18 are exposed, lagging members 20 are installed. When the level of wale 32 is reached, the same is connected to piles 18 and a row of tie-backs 44 is installed. Likewise, when the level of wale 30 is reached, the same is connected to piles 18 and another row of tie-backs 44 is installed. Thereafter, when the level of wale 28 is reached, wale 28 is installed as is a horizontal row of rakers 38. Appropriate trenches are dug to facilitate the latter while piles 18 are still supported by earth yet to be excavated. Thereafter the excavating is completed down to the surface 12.

Tie-backs such as 44 must be anchored behind and beneath the theoretical plane of slippage. Hence, but for the resistive action of rakers 38 and the resultant elevation of th theoretical plane of slippage (from 24 to 42) the anchors 50 would have to be positioned entirely behind plane 24 at a resultant substantial increase in cost. Furthermore, the foundation of an adjacent structure might well prevent such positioning of the anchors. On the other hand, but for the use of tie-back elements 44, additional rakers would have to be used to shore wales 30 and 32 externally of face 14. Manifestly, such additional rakers would interfere with the process of excavation.

By use of the prior art methods, as the excavation proceeded, either extremely long rakers would be installed and further excavation would be impeded, or extremely long and expensive tie-backs would be installed. By use of th present invention, relatively short tie-backs are utilized, and excavation proceeds unimpeded. Likewise, further savings are made when the level of wale 30 is reached. Since tie-backs 44 support the upper portion 43 of wall 27, only the lower portion 36 thereof need be reinforced by rakers and therefore, rakers 38 are relatively shot and present little obstruction to the remainder of the excavating. Hence, the present invention provides a method for reinforcing excavations which is adapted for substantially universal application and substantially decreases constructional costs.

What is claimed is:

1. A method of shoring a sheeting wall which reinforces an upright earthen face adjoining an excavation, said method comprising the steps of:

internally supporting an upper portion of said wall by emplacing anchors in the earth spaced behind the wall and connecting a tendon between said upper portion and each of said anchors, said tendons extending angularly downwardly into the earth behind said wall; and externally supporting a lower portion of said wall by connecting rakers between the bottom of the excava= tion and locations on said lower portion which are spaced apart and spaced above the bottom of the excavation, said rakers extending angularly downardly from said wall into the excavation and having sufficient compressive strength to raise the theoretical plane of earth slippage from its normal location along a first plane intersecting the sheeting wall at the bottom of the excavation to a second plane intersecting the sheeting wall near the raker connections to said wall, each of said anchors being emplaced with at least a major portion thereof positioned between said first and second planes.

2. A method according to claim 1 wherein the upper ends of said anchors are emplaced near said second plane.

3. A method according to claim 1 wherein said anchors are emplaced entirely above said first plane.

4. A method according to claim 1 wherein said rakers are connected to said wall along a generally horizontal row.

5. A method according to claim 4 wherein said rakers are connected to the lower one-third of said wall.

6. A method according to claim 4 wherein said tendons are connected to said wall along a generally horizontal row.

7. A method according to claim 6 wherein said anchors and tendons are emplaced in a plurality of vertically spaced generally parallel planes.

8. A structure reinforcing an upright earthen face adjoining an excavation, said structure comprising:

a sheeting wall bearing against said face;

a plurality of rakers connected between the bottom of the excavation and locations on a lower portion of said wall which are spaced apart and spaced above the bottom of said excavation, said rakers extending angularly downwardly from said wall into the excavation and having sufiicient compressive strength to externally support said lower portion and raise the theoretical plane of earth slippage from its normal location along a first plane intersecting the sheeting wall at the bottom of the excavation to a second plane intersecting the wall near the raker connections to said wall; and

a plurality of tie-backs internally supporting an upper portion of said wall, each of said tie-backs including an anchor disposed in the earth spaced behind said wall with at least a major portion of the anchor positioned between said first and second planes and a tendon extending angularly downwardly into the earth behind said wall and connecting the upper portion of said wall to said anchor.

9. A structure according to claim 8 wherein said anchors are elongated and extend angulary downwardly from near said second plane in alignment with corresponding tendons.

10. A structure according to claim 8 wherein said anchors are disposed entirely above said first plane.

11. A structure according to claim 8 wherein said rakers are connected to said wall along a generally horizontal row.

12. A structure according to claim 11 wherein said rakers are connected to the lower one-third of said wall.

13. A structure according to claim 11 wherein said tendons are connected to said wall along a generally horizontal row.

14. A structure according to claim 13 wherein said anchors and tendons are disposed in a plurality of vertically spaced, substantially mutually parallel planes.

15. A structure according to claim 14 wherein said anchors are elongated and extend angulary downwardly from near said second plane in alignment with corresponding tendons.

References Cited UNITED STATES PATENTS 3,226,933 1/1966 White 61-39 3,243,963 4/1966 Schnabel 61-39 3,250,075 5/1966 Webb et al. 61-39 JACOB SHAPIRO, Primary Examiner US. Cl. X.R. 

